1. Field of the Invention
This invention relates to a bearing used in a small motor for an information-processing device, and particularly to a rolling bearing of a small motor for an information-processing device, optimal as a small motor for which high-speed rotation is required, such as in the case of a HDD spindle motor.
2. Description of the Related Art
Initial acoustic performance, low torque and long-term acoustic durability performance are required for the bearing of an information-processing device, such as the bearing of a high-speed rotating HDD spindle motor.
Particularly, in recent years, the motor used for a large-capacity HDD, such as a server, is used as high speed rotation such as 15,000 rpm to 20,000 rpm, and as the speed increases, the heat produced by rotation of the bearing itself increases, so that the condition of lubrication inside the bearing becomes very inadequate for maintaining acoustical life over a long period of use.
Therefore, conventionally, the surface pressure resulting from pre-loading during use of the bearing was taken into consideration, and the maximum value for a deep-groove ball bearing given in Japan Industrial Standard JIS1519 is applied for the groove radius ratio of the raceway groove of the inner and outer-races of a conventional bearing for an information-processing device, and generally, the groove radius ratio for the raceway groove of an inner-race is set at 52%, and the groove radius ratio for the raceway groove of an outer-race is set at 53%.
Here, the “groove radius ratio” is the ratio of the groove radius of the raceway surface with respect to the ball diameter (groove radius/ball diameter).
In the case of the conventional bearing mentioned above, as the rotation member during use increases, the heat generated by the bearing causes the lubrication condition inside the bearing to become poor, resulting in that wear on the raceway surfaces of the inner and outer-races progresses, and when the bearing is used for a long period of time, there is a possibility that problems with the acoustic life could occur.